Electric cable



March 24, 1936.

R. A. SCHATZEL ELECTRIC CABLE Filed NOV. 2l, 1952 MTC Patented Mar. 24, 1936 UNITED STATES ,PATENT OFFICE ELECTRIC CABLE a corporation of New Jersey Application November 21, 1932, Serial No. 643,641

13 Claims.

This invention relates to electrical conductors for carrying heavy electrical loads of relatively low voltage such as are encountered, for example, in network distribution systems such as are now commonly employed for current distribution in congested areas.

Under the conditions encountered in such systems, if any break-down occurs -in the insulation a destructive arcing is established between the affected conductor and' the ground; or between the conductor and the metallic sheath, where such sheath is employed; or between separate conductors. Because of the intensity of the current carried by network cables, such an arc may continue for some time and does usually continue until the conductor itself has burned off to a point where the arc is so extended in length that it can not be maintained by the impressed voltage. With the usual type of conductors such arcing destroys the insulation and produces a rapid generation of explosive pressures, blowing off manhole covers throughout the adiacent area and otherwise establishing a very dangerous situation.

An object of this invention is to provide an insulated electrical conductor, particularly adapted for network distribution systems, constructed and arranged to reduce the burn-off period to such a short length of time as to forestall the generation of explosive pressures and to prevent injury to the associated system.

This and other objects which will be apparent tc those skilled in this particular art are attained by the present invention which is illustrated in the accompanying drawing which shows a network cable having a protective and insulating covering constructed in accordance with one embodiment of this invention.

The present invention includes the provisionof a shield or mask of non-combustible material having a high fusing point around the metallic conductor to intercept and quench an arc formed in case of breakdown. This shield or mask is in turn surrounded by a moisture seal containing a minimum of organic materialfor the purpose of protecting the mask against moisture, and a protective outer sheath surrounds the whole.

As illustrated, the present invention is shown in connection with an electrical conductor l which may be of any desired type or arrangement, but which is shown as a standard stranded conductor. Immediately surrounding the conductor is a layer 2 of name-resistant or non-inflammable material having a high fusing point and preferably consisting of asbestos either in the form of a braid or a layer of unsaturated asbestos ber. In the case of liber itrmay be arranged as a felted layer, or it may be applied in the form of roving. In whatever form the asbestos is used, it provides a non-inammable ,f layer or mask tightly enclosing the conductor l to prevent access of air to the conductor. The flame-resistant layer is in turn enclosed within a moisture seal preferably formed by a layer 3 of a rubber compound which may comprise a mixture of approximately dry mineral ash or similar non-inflammable material and approximately 20% rubber. Such a compound vconstitutes a moisture seal for protecting the conductor and non-iniiammable shield 2 against moisture and also acts as an electrical insulating layer. One such compound which will be found satisfactory consists of the following ingredients in approximately the proportions by weight shown:

Rubber 20 Sulphur .625 Captax .094 Litharge 3.0 Zinc oxide 30.125 Whiting 44 Parain 2.00 Stearic acid .50

The moisture seal also includes a layer of rubberized tape 4 which is applied directly over the rubber compound 3. The tape and moisture sealing compound compress the layer of asbestos into close engagement with the conductor I and prevent air having access thereto. The moisture seal is in turn covered by a surrounding layer 5 of asbestos or a flame-resistant mixture of asbestos and cotton which is preferably in the form of a braid but which may be applied as a felted layer or in the form of roving. 'Ihe covering 5 over the moisture seal forms a name-resistant baille which will eiectively smother any substantial combustion of the moisture seal should any flame lodge there.

In the preferred embodiment of this invention the conductor is provided with a non-metallic protective sheath 6, although the invention is obviously adaptable to metallic sheathed cables. As illustrated the non-metallic sheath is formed by a cotton braid 6 saturated with a flame-proof saturant 'I and finished with a name-proof paint 8. In the case of metallic sheathed cables the lead sheath will be applied ordinarily directly over the non-inflammable protective layer 5. However, for use in conventional network systems, especially where the conductors are located in ducts, the non-metallic sheath will usually be preferable, as the alkalies, sewage and the like which collect in city manholes rapidly destroy the lead sheaths of metallic sheathed cables. With such a cable as that above described if any breakdown occurs in the insulation such as would establish a destructive arc, the inner layer of asbestos 2 protects the rubber insulation from the arc and prevents any substantial burning thereof, thus reducing the generation of explosive pressures and of destructive gases to a minimum. Similarly, the inner layer of asbestos 2 forms a mask or baille around the conductor I and hastens quenching of the arc. At the same time, the outer layer 5 of asbestos co-operates with the inner layer 2 to prevent access of air to the rubber insulation 3 and prevents combustion thereof in this manner. As a result, the arc is quickly quenched and the entire system protected against prolonged burn-off periods such as have heretofore been common.

While the present invention is equally adaptable to copper or aluminum conductors, a network cable having the most desirable burn-off characteristics is obtained by incorporating therein an aluminum conductor. In such an arrangement, the effect of the asbestos mask in quenching and blanketing the arc thereby is augmented by the aluminum which, having a lower melting point and a higher electrical resistance than copper will burn clear at a lower current density than is the case with copper, and in a shorter time, thus cooperating with the asbestos mask and augmenting the operation of the mask in localizing the fault. At the same time volatilization of an aluminum conductor produces an aluminum oxide which is a very poor electrical conductor and which increases resistance to the arc thereby also co-operating with the asbestos mask in quenching the arc. At the same time the formation of the aluminum oxide renders it extremely difficult for an arc to become reestablished after it has once been extinguished.

I claim:

1. An article of manufacture comprising an electrical conductor, a tightly compressed layer of unsaturated asbestos surrounding said conductor, a moisture seal over said asbestos, an outer layer of non-inflammable material, and a protective flame-resistant sheath.

2. An article of manufacture comprising an electrical conductor, a layer of asbestos surrounding said conductor, a moisture seal surrounding said layer comprising a rubber compound having embodied therein a high percentage of dry noninammable mineral to increase materially the resistance thereof to deterioration by heat, and a protective flame-resistant sheath.

3. An article of manufacture comprising in combination an electrical conductor, a layer of material having a high fusing point surrounding said conductor, a moisture seal surrounding said material and comprising a compound of rubber having approximately 80% dry non-inflammable mineral embodied therein, an outer layer of noninammable material surrounding said moisture seal, and a protective sheath surrounding the Whole.

4. An article of manufacture comprising in combination an aluminum conductor, a layer of material having a high fusing point surrounding said conductor, a moisture seal surrounding said material and comprising a compound of rubber having approximately 80% dry non-inflammable mineral embodied therein, an outer layer of noninliammable material surrounding said moisture seal, and a protective sheath surrounding the whole.

5. An article of manufacture comprising in combination an electrical conductor, an unsaturate-6. layer of non-inflammable fibrous material having a fusing point higher than that of the conductor surrounding said conductor, a moisture seal surrounding said material, and a protective cover surrounding said moisture seal and including an outer braid having a llame-proof saturant and an outer coating of flame-proof paint.

6. An article of manufacture comprising in combination an aluminum conductor, a layer of non-inflammable material having a high fusing point surrounding said conductor, a moisture seal surrounding said material comprising a compound of rubber having dry non-inflammable mineral embodied therein, a layer of flame-resistant material surrounding said moisture seal, a protective sheath comprising a braided jacket having a flame-proof saturant incorporated therein and an outer coating of flame-proof paint.

7. An article of manufacture comprising an electrical conductor, a layer of asbestos fiber surrounding said conductor, a moisture seal surrounding said layer and comprising a rubber compound containing a high percentage of non- 'inilammable mineral, a second layer of asbestos containing material surrounding said moisture seal, an outer protective braid including a flameproof saturant, and a coating of ilame-proof paint.

8. An article of manufacture comprising an electrical conductor, a surrounding layer of insulating material which is non-combustible at the temperature of an electric arc, a separate and distinct layer of insulating material surrounding the first layer of insulating material constituting a moisture seal to prevent penetration of any external moisture to the inner insulating layer, said second layer of insulating material comprising an inflammable material having embodied therein a large proportion of noninfiammable material to increase materially the resistance thereof to deterioration by heat, and an extra protective sheath preventing access of air to the outer surface of the second insulating layer.

9. An article of manufacture comprising an electrical conductor, a surrounding layer of unsaturated, brous insulating material which is non-combustible at the temperature of an electric arc, a separate and distinct layer of insulating material surrounding the first layer of insulating material constituting a moisture seal to prevent penetration of any external moisture to the inner insulating layer, said second layer of insulating material comprising an inflammable material having embodied therein a large proportion of non-inammable material to increase materially the resistance thereof to deterioration by heat, and an outer protective sheath preventing access of air to the outer surface of the second insulating layer. i

l0. An article of manufacture comprising an electrical conductor, a surrounding layer of fibrous insulating material which is non-combustible at the temperature of an electric arc,

y a separate and distinct layer of insulating material surrounding the first layer of insulating material constituting a moisture seal to prevent penetration of any external moisture to the inner insulating layer, a layer of llame-resistant material surrounding the second insulating layer, and an outer protective sheath preventing access of air to the insulating layers.

11. An article of manufacture comprising an electrical conductor, a surrounding layer of combustible insulating material, an outer enclosing sheath resistant to combustion and to the penetration of air and moisture, and combustionsmothering masks of unsaturated, non-combustible, felted, brous insulating material separating the combustible insulating material from the conductor and from the outer sheath.

i2. An article of manufacture comprising an electrical conductor which comprises material capable of quickly forming a relatively non-conductive oxide in the presence of an electric arc to extinguish an arc caused by arcing conditions, a surrounding layer of combustible insulating material having embodied therein a large proportion of non-inflammable material to increase materially the resistance thereof to deterioration by heat, a combustion-smothering mask of noncombustible insulating material separating the conductor and the combustible insulating mateterial, and an outer name-resistant protective sheath surrounding the combustible insulating material.

13. An article of manufacture comprising an aluminum conductor, a surrounding layer of combustible insulating material having embodied therein a large proportion of non-inflammable material to increase materially the resistance thereof to deterioration by heat, a combustionsmothering mask of non-combustible insulating material separating the conductor and the combustible insulating material, and an outer iiameresistant protective sheath surrounding the combustible insulating material.

RUDOLPH A. SCHATZEL. 

